[InstCombine][NFC] add2.ll: add a few commutative checks.

Fixes some missing test coverage in InstCombineAddSub.cpp, visitAdd()

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330986 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed